I'm always amazed how much better my performance is after I come back from being sick (you know, after a couple little "weak" days in the gym while my body remembers that we like to lift

I would say that almost all of my PR's are set at a point where I have been working hard for weeks, then I am forced to take a few easy workouts (sick, vacation, etc.) then when I come back POW right through my old PR's in a big way.